1. Field of the Invention
This invention relates to a photocathode and more particularly to a photocathode comprising rubidium, cesium and antimony, and to methods of forming such a photocathode.
2. Description of the Prior Art
The rubidium-cesium-antimony (Rb-Cs-Sb) photocathode, useful in phototubes and other high vacuum photomultiplier tubes, has been known for some time. The particular advantages of this photocathode over the commonly used S-11 (Cs-Sb), (K.sub.2 CsSb) and (Na.sub.2 KSb) photocathodes have been found to be in its better properties of long wavelength threshold, luminous sensitivity and relative ease of processing. (See Carl W. Morrison, "Technique For Producing High Sensitivity Rubidium-Cesium-Antimony Photocathodes", Journal of Applied Physics, Volume 37, Number 2, February 1966, pages 713-715.)
It has also been determined that the sensitivity and threshold wavelength of Rb-Cs-Sb photocathodes are increased by the well-known process of superficial oxidation. However, the sensitivities of these photocathodes produced by the common prior art techniques, including superficial oxidation, disadvantageously vary within a wide range from about 30 to 120 microamperes per lumen. Such a broad range of photocathode sensitivities generally results in unacceptable non-uniformities in tube performance and relatively high scrap rates due to failure to meet required sensitivity levels. It is therefore desirable to consistently make photocathodes of relatively high sensitivity without superficial oxidation for ease of processing and improvement in performance.